There is no problem more
at the heart of developmental psychology than how to explain individual
differences. Why do some children succeed in school while others do not, why
are some agreeable and others not, why do some fall into criminality and others
not, why do some develop stable relationships and others do not? The list is
very long. During the first three-quarters of the twentieth century there were
three dominant approaches to these issues in Anglo-American psychology, the
psychoanalytic model due to Freud, the (maternal) attachment model represented
by Bowlby and others, and the behaviorist approaches of Watson and Skinner.
All three shared a belief that the role of genes was not of consequence and
thus that the answers were to be found in environmental conditions. The first
two agreed that, because the child was most susceptible to influence when very
young, the effects of parenting outweighed all other environmental causes. In
the final quarter of the century a fourth tradition, behavioral genetics, arose
to challenge the others.

Genetic influence upon child
development can be shown rather straightforwardly although the logistics of the
research is formidable: First, if genes were inconsequential, identical twins
reared together would display far greater correlation for key traits than
identical twins reared apart, but this is not the case. Second, if genes were
inconsequential, differences in levels for key traits between identical twins
as compared to fraternal twins would not be significant, but this is not the
case. Finally, if genes were inconsequential, children adopted at birth would
become more similar in interests to their adopting parents than to their
biological parents, but this is not the case. Eleanor Maccoby notes in the
text under review, "Behavior geneticists have made their case … [that] …
genetic factors do clearly make a significant contribution to individual
differences …"(37).

But behavioral genetics had a
second cherished belief to critique, that the family is the most efficacious of
the environmental factors prompting individual differences. The behavioral
genetic critiques of earlier research were clearly reported in David C. Rowe's The
Limits of Family Influence (Guilford Press, 1994), but it was Judith Rich
Harris' The Nurture Assumption: Why Children Turn Out the Way They Do
(The Free Press, 1998) that brought the matter to a head.

The text under review contains the
follow-up papers of a conference held in August 1999, a gathering planned,
according to the preface, to address one of Harris' conclusions, to wit,
"the assumption that what influences children's development, apart from
their genes, is the way their parents bring them up … is wrong" (xiii).
It has been a decade since Rowe's semi-popularized review of these conclusions
and still Harris' statement remains shocking to read. It is fitting then that
the text would begin with chapters first by Harris and then by Rowe who
together outline the case against the importance of family influence.

A common way of approaching the
question of individual differences is to wonder why siblings from the same
family are so unalike. It cannot be birth order since fraternal twins are so
different and it cannot be genetics alone because the personality correlation
for identical twins reared together is only about 50%. As evidence of the
limited influence of family environment Harris notes first that researchers
have not turned up any significant personality differences between children who
have and those who do not have siblings despite the fact that the family lives
of these two children are so different. Second, no important differences have
been found between children beginning daycare in early infancy and those whose
first three years were with a parent. Third, children in the U. S. raised in a
non-English speaking family will adopt English and not the family language as
primary. Finally, Harris reviews the literature showing that behaviors learned
and developed in one social context do not readily transfer to another. She is
critical of intervention studies that teach effective home parenting but do not
objectively assess behavioral changes in other contexts such as the school.
"… my survey of the intervention literature led me to conclude that
home-based interventions cannot improve children's behavior at school …"
(17).

David Rowe's essay focuses on what
twin and adoption research reveals about parenting efficacy. He is critical of
studies manifesting correlations between certain parenting behaviors and
measures of child outcomes, e.g., that children of parents who read to them
consistently manifest superior verbal skills. These studies fail to control
for genetic similarities (parent and child share genotypes that increase reading
behavior), and fail to control for child-to-parent effects (the child gets read
to because she is genetically disposed to love stories and so reinforces the
parent who reads to her.)

The existence and scope
of child-to-parent effects turns the old assumption about the importance of the
specifics of parenting styles on its head. Lab studies show that parents pay
more attention to physically attractive children (26). Fraternal twins receive
less equal parental attention than identical twins (27). In one study,
researchers found that children born of biological mothers with high risk
behavior characteristics and adopted out early in life received more negative
control from the adopting parents than did children of less risky mothers.
This was true despite the fact that the adopting parents had no knowledge of
the risk levels (30). The conclusion is not that the adopting parents of the high
risk children were predisposed to be severe in their parenting or that
parenting severity causes negative child behaviors but that the negative
behaviors of the child prompted negative parenting behaviors. Finally on the
matter of the weakness of shared environment to make siblings alike Rowe notes
that adopted siblings who share the same home environment from infancy have
very different behaviors (31). The conclusions suggested by the Harris and
Rowe contributions are that (1) genetics plays a significant role in individual
differences, (2) previous research that seemed to establish parent-to-child
effects was flawed on a number of counts, and (3) there is little evidence to
support long term parent-to-child effects.

In her The Nurture Assumption
Harris makes important use of the work of Eleanor Maccoby, particularly her
article, with John Martin, "Socialization in the Context of the Family:
Parent Child Interaction" in E. M. Hetherington, ed. (1983) Handbook of
Child Psychology, vol. 4. (New York: Wiley). Harris paraphrases from the
conclusions of the Maccoby and Martin literature review, "Either … parents
have no effect or that they have different effects on each of their children
…" (Harris 1998 p. 38). Harris notes, somewhat dramatically to be sure,
"With a stroke of the pen, Maccoby and Martin had crossed out most of the
things that socialization researchers had been making a living on for
decades" (39). It seems to make sense therefore that Maccoby should
follow the chapters by Harris and Rowe, though the outcome is unexpected.

She begins with the claim
that textbook writer Harris' 1998 critique of the state of developmental
psychology was "out of date" (35) noting that "Popular
psychology books and elementary textbooks are usually somewhat behind the most
recent research" (36). This claim is hard to square with Harris'
citations. For example her critique of Baumrind's program of authoritarian,
permissive, authoritative parenting styles contains references from 1989
through 1996. Her critique of the research citing the dire effects of divorce
on children contains citations mostly from the 1990's.

But Maccoby is most interested in
refuting the assertion that while different (unshared) environments conspire to
make children different, shared environments do not seem to affect children –
or at least do not conspire to make them similar. Part of Maccoby's argument
rests upon a methodological critique of the reliance by behavioral geneticists
on the concept of heritability or h2. For example the h2
of IQ is .60 to .80 partly on the evidence that the IQ of a child adopted at
birth will correlate with the IQ of the biological and not the adopting
parent. This leads the behavioral geneticist to conclude little or no effect
of the adoptee's family life on IQ. But Maccoby notes that the correlational
nature of the h2 measure hides the well-known fact that IQs of
adopted children are consistently higher than those of their biological
parent. She notes further that late adopted children gain IQ points between
age 4 and adolescence and that the size of the gain correlates with the
socioeconomic status into which the child is adopted. (38-40). Maccoby could
also have mentioned the mysterious "Flynn effect," the fact that in
some European countries IQ scores are increasing over generations at an amazing
rate. (Flynn, J. R. (1987). "Massive IQ gains in 14 nations: What IQ
tests really measure". Psychological Bulletin, 101, 171-191. But
while this argues for environmental effects upon IQ (the same arguments could
be made for adult body height), it does not make a case for family causes.
Children adopted into higher socioeconomic status probably do experience a
cognitively enriched home life, but they also attend better schools, have more
verbal play mates, etc. Maccoby's chapter is clear and interesting and it
provides a good counter to the Harris and Rowe views.

Sharon Landesman Ramey in chapter 4,
decries the book publishers and corporations who tout new "scientifically
based" ideas and products that either promise more than they can provide
or raise sweeping questions about whether parents or early childhood experiences
really matter. "Such distortions serve to misguide or confuse parents
…" (49). Ramey names none of the evildoers in these regards but it would
be difficult not to speculate that she has Harris' book prominently in view.
Of course no one seriously proposes that the quality of parenting does not
matter to a child, except perhaps those who think that parenthood equates to
shaping the enduring traits of the adult whom the child is to become. And
questioning the importance for later development of early experiences within
normal ranges is hardly radical, amounting as it does to the not-very-novel
idea that children are more resilient that some traditions have asserted. (for
example see, Kagan, Jerome. (1998). Three
Seductive Ideas. CambridgeMA: HarvardUniversity Press.)

But Ramey makes a point about child
development research, including the search for parenting effects, that is often
missed. This is that the focus is almost entirely on the explanation of
"stable traitlike qualities", intelligence or personality for
example. If one is in search of parenting effects this focus rules out many
features of the adolescent that may be a function of parenting parenting
practice. She mentions the child's knowledge base, his health promoting
behaviors, spiritual belief systems, art and music appreciation, and more. The
point is very important. Two young adults could score identically on the
"big five" personality sprectra of extraversion, agreeableness,
conscientiousness, emotional stability and intellectual openness and still live
vastly different lives if one had been enthusiastically introduced to some
subset of cooking, motor repair, sailing, golf, opera, plumbing, hiking, fine
dining, fishing, motorcycling, carpentry, sewing, film, religious worship,
archaeology, and more, while the other had few or none of these interests.

Philip Cowan and Carloyn Pape Cowan
argue that studies of family interventions can show parent-to-child effects in
ways that other approaches cannot. This is particularly interesting because
such studies are very close to an experimental model of parenting and child
development research. They note that research in the field can look at
concurrent correlations such as those between authoritative parenting and
academic success, or retrospective designs such as relationships between early
spanking and later aggression, or prospective longitudinal studies. But all of
these have problems with the directions of causation and with controlling for
genetic effects (77-81). Intervention designs have a chance of overcoming
these pitfalls and the results from the other three are useful in the framing
of the intervention research . The most interesting result from their own
research is that interventions that included significant discussions of marital
issues as well as parenting instruction were the most successful. Cowan and
Cowan note, "It is not only what parents do with or to the child that
matters, but how the parents behave with each other." (94)

There is much more to like about
the chapters in this text. Kenneth Dodge takes on Sandra Scarr's well-known
claim that individual differences in early parenting, in normal situations,
have little long-term effect upon enduring traitlike individual differences.
(Scarr, Sandra (1992). "Developmental Theories for the 1990s: Development
and individual differences. Child Development, 63, 1-19.) Dodge
questions whether we can draw clear boundaries of normality, noting from
statistics on poverty, single motherhood, prenatal care, and the lifetime sexual
abuse of females (1 in 3) that Scarr's "normal" qualifier would rule
out fully one half of American children. This seems wrong on two fronts. First
his examples are faulty. The oft-cited 1 in 3 statistic, even if true and I
doubt it, refers not to children but to lifetimes, raising a child as a single
parent hardly qualifies as parenting outside the ranges of normality, and the
same for parenting while in poverty. More importantly, Scarr is not referring
to a statistical norm. Her view is connected to an evolutionary viewpoint
where every species must have multiple possible environments in which it can
flourish in addition to the others in which it cannot. Humans can live in good
health within the Arctic Circle and at the equator. They would hardly have
survived the rigors of natural selection if as children humans required two
parents, two cars and two siblings. As Scarr puts it, "… variations among
environments that support normal human development are not very important as
determinants of variations in children's outcomes" (Scarr 1992 p. 4).
Dodge also criticizes Scarr's reliance upon behavioral genetic studies that
themselves are tied so closely to means and variances within populations,
ignoring, " … within-individual variation cross-situational variation …
and between-individual dynamic processes …" (217). His third objection is
that, "… it is simply unrealistic to expect that individual differences in
parenting in the first few years of life will have a unique and life-long enduring
effect" (217). My trouble with this last objection to Scarr's position is
that it seems to be exactly Scarr's position. Dodge's positive point is that
what children take away from their immersion in parenting are "storylike"
messages: Can adults be trusted?, Is the world safe?, Can I rely on others?
These messages are stored in memory and, in turn, guide the child's future
interactions and outcomes (226). This is an interesting shift in how to think
about parenting effects, though it needs a good deal of elaboration.

There is much more in this text.
It is a collection of excellent essays that report the best of recent thinking
and is excellently edited. It would be appropriate for upper level
undergraduate courses as well as an early graduate level introduction to the
state of thinking about issues surrounding the parent-to-child effects of
diverse child rearing practices. The text would be interesting as well for
philosophers thinking about methodological and conceptual problems surrounding
the nature-nurture debates. It certainly should be included in the collection
of any good undergraduate library.

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